Low temperature NOx reduction using H2-SCR for diesel vehicles

ABSTRACT

Disclosed herein are emission treatment systems, articles, and methods for selectively reducing NOx compounds. The systems include a hydrogen generator, a hydrogen selective catalytic reduction (H 2 -SCR) article, and one or more of a diesel oxidation catalyst (DOC) and/or a lean NOx trap (LNT) and/or a low temperature NOx adsorber (LTNA). Certain articles may comprise a zone coated substrate and/or a layered coated substrate and/or an intermingled coated substrate of one or more of the H 2 -SCR and/or DOC and/or LNT and/or LTNA catalytic compositions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/IB2017/056452, filed Oct. 17, 2017, which International Applicationwas published by the International Bureau in English on Apr. 26, 2018,and which claims priority to U.S. Provisional Application No.62/409,413, filed on Oct. 18, 2016, the content of each of which ishereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to emission treatment systems andcatalytic articles for selectively reducing NOx compounds. Specifically,emission treatment systems comprising a hydrogen selective catalyticreduction article.

BACKGROUND

Diesel engine exhaust is a heterogeneous mixture which contains gaseous,liquid, and solid emissions such as carbon monoxide (“CO”), unburned orpartially burned hydrocarbons or oxygenates thereof (“HC”) and nitrogenoxides (“NOx”). These emissions are subject to governmental legislation.Therefore, catalyst compositions and substrates on which thecompositions are disposed are provided in diesel engine exhaust systemsto convert certain or all of these exhaust components to innocuouscomponents and reduce the amount of emissions released to theatmosphere.

Presently two commercial technologies are utilized for diesel NOxcontrol; namely, selective catalytic reduction (SCR) of urea withammonia and lean NOx trap (LNT). The SCR technology is used in heavyduty and in light duty applications. LNT technology is used exclusivelyfor light duty applications. These technologies achieve highefficiencies at their operating temperature of about 200° C. or higher.However, at a temperature of about 150° C. or lower, also referred to asthe “cold start” period, these technologies are relatively inefficient.Additionally, these technologies are vulnerable to sulfur poisoning.

NOx emission levels during cold start may also be controlled through NOxstorage (adsorption) and desorption. For example, catalysts may adsorbNOx during the warm-up period and thermally desorb NOx at higher exhausttemperatures. Once higher exhaust temperatures are reached, downstreamcatalysts that convert NOx compounds to innocuous components can operaterelatively efficiently.

With world-wide NOx regulations becoming more stringent and averageengine exhaust temperatures ever decreasing, controlling NOx emissionswith current technologies is becoming more and more challenging.Accordingly, there is a need in the art to identify more effective NOxreduction technologies that are more sulfur tolerant and that may besufficiently effective during cold start operations, i.e., attemperatures of about 150° C. and lower, to meet future stringentregulations.

SUMMARY

In some embodiments, the present disclosure is directed to an emissiontreatment system for selectively reducing NOx compounds, the systemcomprising: a hydrogen generator; and a catalytic article. The catalyticarticle comprising a substrate having a zoned catalytic coating thereon.The zoned catalytic coating comprising an upstream zone comprising anH₂-SCR catalyst composition and a downstream zone comprising a dieseloxidation catalyst (DOC) composition. In other embodiments, thecatalytic article may comprise a substrate having a layered catalyticcoating thereon. The layered catalytic coating comprising a bottom layercomprising a DOC composition and an upper layer comprising an H₂-SCRcomposition. In yet other embodiments, the catalytic article maycomprise a substrate having an intermingled catalytic coating thereon.The intermingled catalytic coating comprising a DOC composition and anH₂-SCR composition. In certain embodiments, the catalytic article maycomprise a substrate having a catalytic coating which combines two ormore of the zoned, layered, or intermingled arrangements. The hydrogengenerator may be positioned in fluid communication and upstream from thecatalytic article.

In some embodiments, the emission treatment system may comprise aseparate H₂-SCR catalytic article comprising a substrate and an H₂-SCRcatalyst composition; and a separate DOC catalytic article comprising asubstrate and a DOC composition. The separate H₂-SCR and DOC catalyticarticles may be incorporated in the system as alternatives to a singlecatalytic article with zoned catalytic coating comprising both a DOC andan H₂-SCR zone. When the H₂-SCR catalytic article and the DOC catalyticarticle are separate, they may be positioned in a fluid communicationwith each other such that the DOC catalytic article is downstream of theH₂-SCR catalytic article. The hydrogen generator may be positioned influid communication and upstream from the H₂-SCR catalytic article.

In some embodiments, the present disclosure is directed to an emissiontreatment system for selectively reducing NOx compounds, the systemcomprising a hydrogen generator; an H₂-SCR catalytic article comprisinga substrate and an H₂-SCR catalyst composition; and a lean NOx trap(LNT) catalytic article comprising a substrate and a LNT catalystcomposition, the LNT catalytic article in fluid communication anddownstream of the H₂-SCR catalytic article, and the hydrogen generatorin fluid communication and upstream of the H₂-SCR catalytic article.

In some embodiments, the present disclosure is directed to a catalyticarticle comprising: a substrate having a zoned catalytic coatingthereon, wherein the zoned catalytic coating comprises: an upstream zonecomprising an H₂-SCR catalyst composition; and a downstream zonecomprising a diesel oxidation catalyst (DOC) composition. In otherembodiments, the catalytic article may comprise a substrate having alayered catalytic coating thereon. The layered catalytic coatingcomprising a bottom layer comprising a DOC composition and an upperlayer comprising an H₂-SCR composition. In yet other embodiments, thecatalytic article may comprise a substrate having an intermingledcatalytic coating thereon. The intermingled catalytic coating comprisinga DOC composition and an H₂-SCR composition. In certain embodiments, thecatalytic article may comprise a substrate having a catalytic coatingwhich combines two or more of the zoned, layered, or intermingledarrangements.

In some embodiments, the present disclosure is directed to a method fortreating an exhaust stream containing NOx, comprising passing theexhaust stream through an emission treatment system or through acatalytic article disclosed herein.

In some embodiments, the emission treatment systems and/or catalyticarticles may further comprise a low temperature NOx adsorbent (LTNA).

In various embodiments where zone coating is used, the upstream zone canoverlay a portion of the downstream zone or the downstream zone canoverlay a portion of the upstream zone. In some cases, the upstream andthe downstream zones are adjacent and do not overlay each other.

Where the LTNA composition is combined with either the H₂-SCRcomposition or the DOC composition, the two compositions can be indirect contact. Where the DOC composition is combined with the H₂-SCRcomposition, the two compositions can be in direct contact.

In various embodiments combining the H₂-SCR composition with the DOCcomposition, the H₂-SCR catalyst composition can extend the entirelength of the substrate and the DOC composition can overlay a portion ofthe H₂-SCR composition. Alternatively, the H₂-SCR catalyst compositioncan extend the entire length of the substrate and the H₂-SCR compositioncan overlay the DOC composition. In other embodiments, the DOC catalystcomposition can extend the entire length of the substrate and the H₂-SCRcomposition can overlay a portion of the DOC composition. Alternatively,the DOC catalyst composition can extend the entire length of thesubstrate and the DOC composition can overlay the H₂-SCR composition.

The present disclosure includes, without limitation, the followingembodiments.

Embodiment 1

An emission treatment system for selectively reducing NOx compounds, thesystem comprising: a hydrogen generator; and an H₂-SCR catalytic articlecomprising a substrate and an H₂-SCR catalyst composition, the hydrogengenerator being in fluid communication with, and upstream of, the H₂-SCRcatalytic article; and at least one of (a) a diesel oxidation catalyst(DOC) catalyst composition; and (b) a lean NOx trap (LNT) composition,wherein when the LNT composition is present, the system comprises a leanNOx trap (LNT) catalytic article comprising a substrate and the LNTcatalyst composition, the LNT catalytic article in fluid communicationwith, and downstream of, the H₂-SCR catalytic article, and wherein whenthe DOC catalyst composition is present, the DOC catalyst composition iseither (1) present in a zoned catalyst coating on the H₂-SCR catalyticarticle with an upstream zone comprising the H₂-SCR catalyst compositionand a downstream zone comprising the DOC catalyst composition; (2)present in an intermingled catalyst coating on the H₂-SCR catalyticarticle comprising the DOC catalyst composition and the H₂-SCR catalystcomposition; (3) present in a layered catalyst coating on the H₂-SCRcatalytic article with a bottom layer comprising the DOC catalystcomposition and an upper layer comprising the H₂-SCR catalystcomposition, or (4) present on a separate DOC catalytic articlecomprising a substrate and the DOC catalyst composition, the DOCcatalytic article in fluid communication with, and downstream of, theH₂-SCR catalytic article.

Embodiment 2

The emission treatment system of any preceding embodiment, furthercomprises a low temperature NOx adsorbent (LTNA) catalyst compositionpresent in either the zoned catalyst coating, the intermingled catalystcoating, or the layered catalytic coating, or present on the H₂-SCRcatalytic article upstream from the separate DOC catalytic article, orpresent on the separate DOC catalytic article.

Embodiment 3

The emission treatment system of any preceding embodiment, wherein, inthe zoned catalyst coating, the LTNA catalyst composition isincorporated into the upstream zone comprising the H₂-SCR catalystcomposition, incorporated into the downstream zone comprising the DOCcomposition, or positioned in a middle zone between the upstream zonecomprising the H₂-SCR catalyst composition and the downstream zonecomprising the DOC composition.

Embodiment 4

The emission treatment system of any preceding embodiment, furthercomprising a low temperature NOx adsorbent (LTNA) catalytic articlecomprising a substrate and a LTNA catalyst composition, the LTNAcatalytic article in fluid communication with the H₂-SCR catalyticarticle and the hydrogen generator.

Embodiment 5

The emission treatment system of any preceding embodiment, wherein theLTNA catalytic article is positioned downstream from the H₂-SCRcatalytic article or positioned upstream from the H₂-SCR catalyticarticle and the hydrogen generator.

Embodiment 6

The emission treatment system of any preceding embodiment, wherein theorder of catalytic articles from upstream to downstream is H₂-SCRcatalytic article, LTNA catalytic article, and DOC catalytic article.

Embodiment 7

The emission treatment system of any preceding embodiment, wherein theorder of catalytic articles from upstream to downstream is H₂-SCRcatalytic article, DOC catalytic article, and LTNA catalytic article.

Embodiment 8

The emission treatment system of any preceding embodiment, wherein theorder of catalytic articles from upstream to downstream is LTNAcatalytic article, H₂-SCR catalytic article, and DOC catalytic article.

Embodiment 9

The emission treatment system of any preceding embodiment, furthercomprising a catalytic soot filter (CSF); a selective catalyticreduction (SCR) catalyst; an ammonia oxidation catalyst (AMOX); orcombinations thereof.

Embodiment 10

The emission treatment system of any preceding embodiment, wherein theSCR catalyst comprises a base metal-containing 8-ring small poremolecular sieve.

Embodiment 11

The emission treatment system of any preceding embodiment, wherein theSCR catalyst comprises an iron- and/or copper-containing 8-ring smallpore molecular sieve.

Embodiment 12

The emission treatment system of any preceding embodiment, wherein themolecular sieve is a zeolite having a structure selected from the groupconsisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV.

Embodiment 13

The emission treatment system of any preceding embodiment, wherein themolecular sieve has a CHA crystal structure.

Embodiment 14

The emission treatment system of any preceding embodiment, wherein thehydrogen generator is selected from the group consisting of on boardhydrogen, hydrogen produced from alcohol reforming, hydrogen producedfrom ammonia decomposition, hydrogen produced from fuel reforming, andcombinations thereof.

Embodiment 15

The emission treatment system of any preceding embodiment, wherein theLNT catalyst composition comprises a NOx sorbent and a platinum groupmetal component dispersed on a refractory metal oxide support.

Embodiment 16

The emission treatment system of any preceding embodiment, wherein theH₂-SCR catalytic article is close coupled.

Embodiment 17

The emission treatment system of any preceding embodiment, wherein theH₂-SCR catalyst composition comprises a platinum group metal componentsupported on a metal oxide or zeolite support.

Embodiment 18

The emission treatment system of any preceding embodiment, wherein theplatinum group metal component is platinum, palladium, or a combinationthereof.

Embodiment 19

The emission treatment system of any preceding embodiment, wherein theplatinum group metal component is supported on a hydrogen form ofzeolite or a metal oxide selected from the group consisting of zirconia,titania, magnesia, and combinations thereof.

Embodiment 20

A catalytic article comprising: a substrate having a catalytic coatingthereon comprising an H₂-SCR catalyst composition and, optionally, adiesel oxidation catalyst (DOC) composition, wherein the H₂-SCR catalystcomposition comprises a platinum group metal component supported on ametal oxide or zeolite support.

Embodiment 21

The catalytic article of any preceding embodiment, comprising either (1)a layered catalytic coating comprising a bottom layer comprising the DOCcomposition and an upper layer comprising the H₂-SCR composition; or (2)a zoned catalytic coating comprising an upstream zone comprising theH₂-SCR catalyst composition and a downstream zone comprising the DOCcomposition; or (3) an intermingled catalytic coating comprising theH₂-SCR composition and the DOC composition.

Embodiment 22

The catalytic article of any preceding embodiment, wherein the platinumgroup metal component is platinum, palladium, or a combination thereof.

Embodiment 23

The catalytic article of any preceding embodiment, wherein the platinumgroup metal component is supported on a hydrogen form of zeolite or ametal oxide selected from the group consisting of zirconia, titania,magnesia, and combinations thereof.

Embodiment 24

The catalytic article of any preceding embodiment, wherein the zonedcatalytic coating further comprises a low temperature NOx adsorbent(LTNA) catalyst composition zone, wherein the LTNA catalyst compositionzone is incorporated into the upstream zone comprising the H₂-SCRcatalyst composition, or the LTNA catalyst composition zone isincorporated into the downstream zone comprising the DOC composition, orthe LTNA catalyst composition zone is positioned in a middle zonebetween the upstream zone comprising the H₂-SCR catalyst composition andthe downstream zone comprising the DOC composition.

Embodiment 25

The catalytic article of any preceding embodiment, wherein the layeredcatalytic coating further comprises a LTNA catalyst composition layer.

Embodiment 26

The catalytic article of any preceding embodiment, wherein theintermingled catalytic coating further comprises a LTNA catalystcomposition.

Embodiment 27

A method for treating an exhaust stream containing NOx, comprisingpassing the exhaust stream through the emission treatment system of anypreceding embodiment.

Embodiment 28

The method of any preceding embodiment, wherein the exhaust stream has atemperature that is about 200° C. or lower, about 175° C. or lower,about 150° C. or lower, about 125° C. or lower, or about 100° C. orlower.

Embodiment 29

A method for treating an exhaust stream containing NOx, comprising:introducing hydrogen gas into the exhaust stream (such as an exhauststream from a lean burn engine such as a diesel engine) to form ahydrogen-treated exhaust stream; passing the hydrogen-treated exhauststream through an emission treatment system comprising an H₂-SCRcatalytic article comprising a substrate and an H₂-SCR catalystcomposition, wherein the H₂-SCR catalyst composition comprises aplatinum group metal component supported on a metal oxide or zeolitesupport.

Embodiment 30

The method of any preceding embodiment, wherein the platinum group metalcomponent is platinum, palladium, or a combination thereof.

Embodiment 31

The method of any preceding embodiment, wherein the platinum group metalcomponent is supported on a hydrogen form of zeolite or a metal oxideselected from the group consisting of zirconia, titania, magnesia, andcombinations thereof.

These and other features, aspects, and advantages of the disclosure willbe apparent from a reading of the following detailed descriptiontogether with the accompanying drawings, which are briefly describedbelow. The present disclosure includes any combination of two, three,four, or more of the above-noted embodiments as well as combinations ofany two, three, four, or more features or elements set forth in thisdisclosure, regardless of whether such features or elements areexpressly combined in a specific embodiment description herein. Thisdisclosure is intended to be read holistically such that any separablefeatures or elements of the disclosed invention, in any of its variousaspects and embodiments, should be viewed as intended to be combinableunless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present disclosure, their nature,and various advantages will become more apparent upon consideration ofthe following detailed description, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an emission treatment system according to anembodiment of the invention where the H₂-SCR and the DOC catalysts arecombined in a single catalytic article;

FIG. 2 illustrates an emission treatment system according to anembodiment of the invention where the H₂-SCR and the DOC catalyticarticles are separate;

FIG. 3 illustrates an emission treatment system according to anembodiment of the invention comprising an H₂-SCR article and a LNTarticle;

FIG. 4 shows the NO_(x) conversion for several example embodiments ofH—Y supported Pt/Pd catalysts at 125° C. at 1% H₂ as a function of feedcondition and Pt/Pd ratio;

FIG. 5 shows the NO_(x) conversion for several example embodiments ofH—Y supported Pt/Pd catalysts as function of reaction temperature withFeed 1;

FIG. 6 shows the NO_(x) conversion for several example embodiments ofH—Y supported Pt/Pd catalysts as function of reaction temperature withFeed 2;

FIG. 7 shows the NO_(x) conversion for several example embodiments ofH—Y supported Pt/Pd catalysts as function of reaction temperature withFeed 3;

FIG. 8 shows the NO_(x) conversion for several example embodiments ofWO₃/TiO₂ supported Pt/Pd catalysts at 125° C. at 1% H₂ as a function offeed condition and Pt/Pd ratio;

FIG. 9 shows the NO_(x) conversion for several example embodiments ofWO₃/TiO₂ supported Pt/Pd catalysts as function of reaction temperaturewith Feed 1;

FIG. 10 shows the NO_(x) conversion for several example embodiments ofWO₃/TiO₂ supported Pt/Pd catalysts as function of reaction temperaturewith Feed 2;

FIG. 11 shows the NO_(x) conversion for several example embodiments ofWO₃/TiO₂ supported Pt/Pd catalysts as function of reaction temperaturewith Feed 3;

FIG. 12 shows the effect of CO on NO_(x) conversion at 150° C. forseveral example embodiments;

FIG. 13 shows the effect of C₃H₆ on NO_(x) conversion at 150° C. forseveral example embodiments;

FIG. 14A is a perspective view of a honeycomb-type substrate which maycomprise a catalyst composition of the invention;

FIG. 14B is a partial cross-sectional view enlarged relative to FIG. 14Aand taken along a plane parallel to the end faces of the carrier of FIG.14A, which shows an enlarged view of a plurality of the gas flowpassages shown in FIG. 14A;

FIG. 15 shows a cross-sectional view of a section of a wall flow filtersubstrate which may comprise a catalyst composition of the invention;and

FIG. 16 shows a cross-sectional view of a substrate having a zonedcatalytic layer.

DEFINITIONS AND MEASUREMENTS

The term “catalytic article” refers to an element that is used topromote a desired reaction. The present catalytic articles comprise asubstrate having a catalytic coating disposed thereon.

The term “exhaust stream” or “exhaust gas stream” refers to anycombination of flowing gas that may contain solid or liquid particulatematter. The stream comprises gaseous components and is for exampleexhaust of a lean burn engine, which may contain certain non-gaseouscomponents such as liquid droplets, solid particulates and the like. Anexhaust stream of a lean burn engine typically further comprisescombustion products, products of incomplete combustion, oxides ofnitrogen, combustible and/or carbonaceous particulate matter (soot) andun-reacted oxygen and/or nitrogen.

The term “catalyst” refers to a material that promotes a chemicalreaction. The catalyst includes the “catalytically active species” andthe “carrier” that carries or supports the active species. For example,molecular sieves including zeolites are carriers/supports for presentcopper and iron active catalytic species. Likewise, refractory metaloxide particles may be a carrier for platinum group metal catalyticspecies.

The term “in fluid communication” is used to refer to articlespositioned on the same exhaust line, i.e., a common exhaust streampasses through articles that are in fluid communication with each other.Articles in fluid communication may be adjacent to each other in theexhaust line. Alternatively, articles in fluid communication may beseparated by one or more articles, also referred to as “bricks.”

The inlet end of a substrate is synonymous with the “upstream” end or“front” end. The outlet end is synonymous with the “downstream” end or“rear” end. An upstream zone is upstream of a downstream zone. Anupstream zone may be closer to the engine or manifold, and a downstreamzone may be further away from the engine or manifold.

“Platinum group metal components” (PGM) refer to platinum group metalsor compounds thereof, for example or one of their oxides. “Rare earthmetal components” refer to one or more oxides of the lanthanum seriesdefined in the Periodic Table of Elements, including lanthanum, cerium,praseodymium and neodymium.

Weight percent (wt %), if not otherwise indicated, is based on an entirecomposition free of any volatiles, that is, based on solids content.

The term “NOx” refers to nitrogen oxide compounds, such NO and NO₂.

DETAILED DESCRIPTION

The present disclosure relates to emission treatment systems, catalyticarticles, and methods for selectively reducing NOx compounds. Thesystems have an upstream H₂-SCR catalytic article and downstreamcatalytic articles that may include one or more of a DOC, LNT, LTNA,SCR, SCR on filter (SCRoF), catalytic soot filter (CSF), and ammoniaoxidation catalyst (AMOX).

FIGS. 1-3 describe three different embodiments of the invention. Thevarious embodiments include a hydrogen generator (150, 250, 350) and aH₂-SCR, such that the hydrogen generator produces an effective amount ofhydrogen to selectively reduce the NOx compounds level by about 5% ormore, about 10% or more, about 20% or more, about 30% or more, about 40%or more, about 50% or more, about 60% or more, about 70% or more, about80% or more, or about 90% or more.

Hydrogen Generator

The hydrogen generator could vary and may be selected from the groupconsisting of on-board hydrogen, hydrogen produced from alcoholreforming, hydrogen produced from ammonia decomposition, hydrogenproduced from hydrocarbon reforming, and mixtures thereof.

Generating hydrogen from on-board hydrogen may require a hydrogenstorage on board.

Generating hydrogen from alcohol reforming may require alcohol storageon board. Suitable alcohols include but are not limited to ethanol andmethanol. The alcohol storage may by connected to a reforming catalystwhich could catalytically reform the ethanol and/or methanol and/orother suitable alcohol to hydrogen.

Generating hydrogen from ammonia decomposition may require on-board ureastorage. On-board urea storage already exists and is utilized to injecturea into the exhaust stream right before the SCR catalytic articleplacement. Thus, a single on-board urea storage may be employed fordifferent purposes. One purpose could be the urea injection into theexhaust stream prior to SCR placement. The other purpose could be a ureainjection used to decompose ammonia and generate hydrogen in the exhauststream prior to the H₂-SCR catalytic article placement.

Hydrogen may also be generated from hydrocarbon reforming. The dieselfuel storage may be connected to a reforming catalyst which couldcatalytically reform hydrocarbons in the diesel fuel to hydrogen. Thishydrogen generator may be more challenging than other hydrogengenerators described due to the diversity of hydrocarbons in the fuel.

It is to be understood that the present invention encompasses varioushydrogen generators and that the above list is exemplary and is notintended to be limiting.

Emission Treatment Systems and Articles

FIG. 1 illustrates an emission treatment system for selectively reducingNOx compounds according to an embodiment. The system comprising: ahydrogen generator 150; and a catalytic article 105. The hydrogengenerator may be selected from the hydrogen generators describedpreviously and may be associated with a reservoir, a pump, and aninjector 130 positioned upstream from the catalytic article 105 and influid communication with catalytic article 105.

Catalytic article 105 may comprise a substrate having a zoned catalyticcoating thereon. The zoned catalytic coating may comprise an upstreamzone comprising an H₂-SCR catalyst composition and a downstream zonecomprising a DOC composition.

In certain embodiments, catalytic article 105 may comprise a substratehaving a layered catalytic coating thereon. The layered catalyticcoating may comprise a bottom layer comprising a DOC composition and anupper layer comprising an H₂-SCR catalytic article.

In other embodiments, catalytic article 105 may comprise a substratehaving an intermingled catalytic coating thereon. The intermingledcatalytic coating may comprise a DOC composition and an H₂-SCRcomposition.

In yet other embodiments, catalytic article 105 may comprise a substratehaving a catalytic coating comprising two or more of the followingarrangements: zoned catalytic coating, layered catalytic coating,intermingled catalytic coating, and combinations thereof.

Catalytic article 105 may further comprise a LTNA. The LTNAfunctionality may be part of the DOC composition, part of the H₂-SCRcatalyst composition, part of both the DOC composition and the H₂-SCRcatalyst composition, separate from the DOC composition and from theH₂-SCR catalyst composition, or combinations thereof. For instance, theLTNA may be incorporated into an upstream zone comprising the H₂-SCRcatalyst composition, into the downstream zone comprising the DOCcomposition, into both the upstream zone and the downstream zone,positioned in a middle zone between an upstream zone and a downstreamzone, or combinations thereof. Another example is where the LTNA isincorporated into a bottom DOC composition layer, into a top H₂-SCRcatalyst composition layer, into both bottom and top layers, into aninterlayer between the bottom and top layer, or combinations thereof. Inyet another example, the LTNA may be intermingled with other componentsof the catalytic article.

In some embodiments, the upstream zone, comprising the H₂-SCR catalystcomposition (with or without LTNA functionality), overlays a portion ofthe downstream zone, comprising the DOC composition (with or withoutLTNA functionality). For instance, the H₂-SCR zone may extend from theinlet end toward the outlet end extending about 10%, about 20%, about30%, about 40%, about 50%, about 60%, about 70%, about 80% or about 90%of the substrate length, while the DOC zone may extend from the outletend towards the inlet end extending about 10%, about 20%, about 30%,about 40%, about 50%, about 60%, about 70%, about 80% or about 90% ofthe substrate length. The upstream and the downstream zones may beadjacent and not overlay each other. Alternatively, the H₂-SCR upstreamzone and the DOC downstream zone may overlay each other, forming a third“middle” zone. The middle zone may for example extend from about 5% toabout 80% of the substrate length, for example about 5%, about 10%,about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, orabout 80% of the substrate length. A cross-sectional view of a zonedcatalytic layer on a substrate is shown in FIG. 16 , where three zonesare shown as part of a coating layer on a substrate 12, including anupstream zone 20, an optional middle zone 24, and a downstream zone 28.

The H₂-SCR and DOC zones may be in direct contact with each otherwithout a “middle” overlapping zone. Alternatively, the H₂-SCR and DOCzones may not be in direct contact, forming a “gap” between the twozones. In the case of an “undercoat” or “overcoat” the gap between theSCR and LNT zones is termed an “interlayer.”

In certain embodiments, the H₂-SCR (with or without LTNA functionality)catalyst composition extends the entire length of the substrate and theDOC composition (with or without LTNA functionality) overlays a portionof the H₂-SCR composition. In other embodiments, the H₂-SCR catalystcomposition (with or without LTNA functionality) extends the entirelength of the substrate and the H₂-SCR composition overlays the DOCcomposition (with or without LTNA functionality). For example, the DOCzone may extend from the outlet end towards the inlet end about 10%,about 20%, about 30%, about 40%, about 50%, about 60%, about 70% orabout 80% of the substrate length.

In certain embodiments, the DOC catalyst composition (with or withoutLTNA functionality) extends the entire length of the substrate and theH₂-SCR composition (with or without LTNA functionality) overlays aportion of the DOC composition. In other embodiments, the DOC catalystcomposition (with or without LTNA functionality) extends the entirelength of the substrate and the DOC composition overlays the H₂-SCRcomposition (with or without LTNA functionality). For example, theH₂-SCR zone may extend from the inlet end towards the outlet end about10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70% orabout 80% of the substrate length.

In certain embodiments, a separate LTNA catalytic article comprising asubstrate comprising a LTNA catalyst composition may be positioned influid communication with the catalytic article comprising both a DOCcomposition (with or without LTNA functionality) and H₂-SCR composition(with or without LTNA functionality). The LTNA catalytic article may belocated upstream or downstream of the catalytic article. If the LTNA ispositioned upstream of the catalytic article, it may also be positionedupstream of the hydrogen generator, as the hydrogen generator ispreferably located immediately prior to the H₂-SCR catalyst composition.The LTNA may also be in fluid communication with other components of theemission treatment system, for example, with the hydrogen generator.

The present zones are defined by the relationship of the H₂-SCR and DOCcatalytic coatings. With respect to H₂-SCR and DOC catalytic coatings,there are only an upstream and a downstream zone or there may be anupstream zone, a middle zone and a downstream zone. Where the H₂-SCR andDOC catalytic coatings are adjacent and do not overlap, there are onlyupstream and downstream zones. Where the H₂-SCR and DOC coatings overlapto a certain degree, there are upstream, downstream and middle zones.Where for example, a H₂-SCR zone extends the entire length of thesubstrate and the DOC zone extends from the outlet end a certain lengthand overlays or underlays a portion of the SCR zone, there are onlyupstream and downstream zones.

The H₂-SCR and DOC zones may be in direct contact with the substrate.Alternatively, one or more “undercoats” may be present, so that at leasta portion of the H₂-SCR and DOC zones are not in direct contact with thesubstrate (but rather with the undercoat). One or more “overcoats” mayalso be present, so that at least a portion of the H₂-SCR and DOC zonesare not directly exposed to a gaseous stream or atmosphere (but ratherare in contact with the overcoat).

The interlayer(s), undercoat(s) and overcoat(s) may contain one or morecatalysts or may be free of catalysts.

The catalytic coatings present in the combined H₂-SCR/DOC catalyticarticle may comprise more than one identical layers.

FIG. 2 illustrates an emission treatment system comprising a separateH₂-SCR catalytic article 205 and a separate DOC catalytic article 210instead of a single catalytic article with a catalytic coatingcomprising both a DOC composition and an H₂-SCR catalyst composition asillustrated in FIG. 1 . H₂-SCR catalytic article 205 comprising asubstrate and an H₂-SCR catalyst composition. DOC catalytic article 210comprising a substrate and a DOC composition. When H₂-SCR catalyticarticle 205 and DOC catalytic article 210 are separate, they may bepositioned in a fluid communication with each other such that the DOCcatalytic article is downstream of the H₂-SCR catalytic article.Similarly to FIG. 1 , any of the hydrogen generators 250 describedpreviously may be included in the system. The hydrogen generator may beassociated with a reservoir, a pump, and an injector 230 positionedupstream from H₂-SCR catalytic article 205 and in fluid communicationwith H₂-SCR catalytic article 205.

The emission treatment system of FIG. 2 may further comprise a separateLTNA catalytic article (not shown). The LTNA catalytic article maycomprise a substrate and a LTNA catalyst composition. The LTNA catalyticarticle may be in fluid communication with other components of theemission treatment system, for example, the H₂-SCR catalytic article,the DOC catalytic article, and the hydrogen generator. The order of thearticles may vary. For instance, the order from upstream to downstreammay be H₂-SCR catalytic article, LTNA catalytic article, and DOCcatalytic article. Alternatively, the order from upstream to downstreammay be H₂-SCR catalytic article, DOC catalytic article, and LTNAcatalytic article. In some embodiments, the order from upstream todownstream may be LTNA catalytic article, H₂-SCR catalytic article, andDOC catalytic article. In certain embodiments, the H₂-SCR catalyticarticle and/or the DOC catalytic article present in the emissiontreatment system of FIG. 2 , include a LTNA catalyst composition as anadded LTNA functionality to either or both articles. For instance, anH₂-SCR catalytic article with LTNA functionality may comprise a zonedH₂-SCR catalyst composition and LTNA catalyst composition, a layeredH₂-SCR catalyst composition and LTNA catalyst composition, anintermingled H₂-SCR catalyst composition and LTNA catalyst composition,or combinations thereof. Similarly, a DOC catalytic article with LTNAfunctionality may comprise a zoned DOC catalyst composition and LTNAcatalyst composition, a layered DOC catalyst composition and LTNAcatalyst composition, an intermingled DOC catalyst composition and LTNAcatalyst composition, or combinations thereof.

In zone catalytic coatings, the upstream zone may overlay a portion ofthe downstream zone or the downstream zone may overlay a portion of theupstream zone as described above for the DOC and H₂-SCR catalyticarticle. Alternatively, the upstream and the downstream zones may beadjacent (either in direct contact or with a gap in the middle) and notoverlay each other.

In layered catalytic coatings, a first layer may extend the entirelength of the substrate and a subsequent layer may overlay a portion ofthe first layer. For instance, for H₂-SCR and LTNA layered catalyticcoating, in one embodiment, the H₂-SCR catalyst composition may extendthe entire length of the substrate and the LTNA catalyst composition mayoverlay the H₂-SCR composition entirely or overlay a portion of theH₂-SCR composition. In another embodiment, the H₂-SCR catalystcomposition may extend the entire length of the substrate and the H₂-SCRcomposition may overlay the LTNA composition entirely or overlay aportion of the LTNA composition.

For DOC and LTNA layered catalytic coating, in one embodiment, the DOCcatalyst composition may extend the entire length of the substrate andthe LTNA catalyst composition may overlay the DOC composition entirelyor overlay a portion of the DOC composition. In another embodiment, theDOC catalyst composition may extend the entire length of the substrateand the DOC composition may overlay the LTNA composition entirely oroverlay a portion of the LTNA composition.

FIG. 3 illustrates an emission treatment system comprising a hydrogengenerator 350; an H₂-SCR catalytic article 305 and a lean NOx trap (LNT)catalytic article 310. The H₂-SCR catalytic article 305 comprising asubstrate and an H₂-SCR catalyst composition. The LNT catalytic article310 comprising a substrate and a LNT catalyst composition. LNT catalyticarticle 310 may be positioned in fluid communication and downstream ofH₂-SCR catalytic article 305. Similarly to FIGS. 1 and 2 , any of thehydrogen generators 350 described previously for producing hydrogen maybe included in the system. The hydrogen generator may be associated witha reservoir, a pump, and an injector 330 positioned upstream from H₂-SCRcatalytic article 305 and in fluid communication with H₂-SCR catalyticarticle 305.

The emission treatment systems according to any of the embodimentsdisclosed herein may further comprise a soot filter and/or a selectivecatalytic reduction (SCR) catalyst and/or SCR on filter (SCRoF) and/oran ammonia oxidation catalyst (AMOX) and/or combinations thereof. Thesoot filter may be uncatalyzed or may be catalyzed (CSF). For instance,FIG. 1 depicts, from upstream to downstream, combined H₂-SCR/DOCcatalytic article 105, a CSF catalytic article 110, an SCR catalyticarticle 115 and a combined catalytic article 120 comprising both SCR andAMOX, all in fluid communication with each other. Another example isFIG. 2 , which depicts, from upstream to downstream, a H₂-SCR catalyticarticle 205, a DOC catalytic article 210, a CSF catalytic article 215, aSCR catalytic article 220 and a combined catalytic article 225comprising both SCR and AMOX, all in fluid communication with eachother. Yet another example is FIG. 3 , which depicts, from upstream todownstream, a H₂-SCR catalytic article 305, a LNT catalytic article 310,an SCR on filter catalytic article 315, and an optional SCR catalyticarticle 320, all in fluid communication with each other. These systemsmay be referred to as “multi-brick” systems, where a “brick” may referto a single article, such as a H₂-SCR, or a DOC, or a CSF, or a LNT, oran AMOX, etc.

Various zoned and layered combinations of catalyst compositions areenvisioned in this disclosure. For example, the H₂-SCR catalytic articlecan comprise a zoned H₂-SCR catalyst composition and LTNA catalystcomposition, a layered H₂-SCR catalyst composition and LTNA catalystcomposition, an intermingled H₂-SCR catalyst composition and LTNAcatalyst composition, or combinations thereof. In addition, the DOCcatalytic article can comprise a zoned DOC catalyst composition and LTNAcatalyst composition, a layered DOC catalyst composition and LTNAcatalyst composition, an intermingled DOC catalyst composition and LTNAcatalyst composition, or combinations thereof.

In one embodiment, the H₂-SCR catalytic article comprises a combinationof a zoned H₂-SCR catalyst composition and LTNA catalyst compositionlocated on an upstream and a downstream zone and a layered H₂-SCRcatalyst composition and LTNA catalyst composition located on a bottomlayer and a top layer, and wherein the upstream zone overlays a portionof the downstream zone.

In another embodiment, the H₂-SCR catalytic article comprises acombination of a zoned H₂-SCR catalyst composition and LTNA catalystcomposition located on an upstream and a downstream zone and a layeredH₂-SCR catalyst composition and LTNA catalyst composition located on abottom layer and a top layer, and wherein the downstream zone overlays aportion of the upstream zone.

In certain embodiments, the DOC catalytic article comprises acombination of a zoned DOC catalyst composition and LTNA catalystcomposition located on an upstream and a downstream zone and a layeredDOC catalyst composition and LTNA catalyst composition located on abottom layer and a top layer, and wherein the upstream zone overlays aportion of the downstream zone.

In another embodiment, the DOC catalytic article comprises a combinationof a zoned DOC catalyst composition and LTNA catalyst compositionlocated on an upstream and a downstream zone and a layered DOC catalystcomposition and LTNA catalyst composition located on a bottom layer anda top layer, and wherein the downstream zone overlays a portion of theupstream zone.

In yet another embodiment, the H₂-SCR catalytic article comprises acombination of a zoned H₂-SCR catalyst composition and LTNA catalystcomposition and a layered H₂-SCR catalyst composition and LTNA catalystcomposition, and wherein the H₂-SCR catalyst composition extends theentire length of the substrate and the LTNA catalyst compositionoverlays a portion of the H₂-SCR composition.

In still further embodiments, the H₂-SCR catalytic article comprises alayered H₂-SCR catalyst composition and LTNA catalyst composition, andwherein the H₂-SCR catalyst composition extends the entire length of thesubstrate and the H₂-SCR composition overlays the LTNA composition.

In another embodiment, the H₂-SCR catalytic article comprises acombination of a zoned H₂-SCR catalyst composition and LTNA catalystcomposition and a layered H₂-SCR catalyst composition and LTNA catalystcomposition, and wherein the H₂-SCR catalyst composition extends theentire length of the substrate and the H₂-SCR composition overlays aportion of the LTNA composition.

In other embodiments, the H₂-SCR catalytic article comprises a layeredH₂-SCR catalyst composition and LTNA catalyst composition, and whereinthe H₂-SCR catalyst composition extends the entire length of thesubstrate and the LTNA composition overlays the H₂-SCR composition.

In certain embodiments, the DOC catalytic article comprises acombination of a zoned DOC catalyst composition and LTNA catalystcomposition and a layered DOC catalyst composition and LTNA catalystcomposition, and wherein the DOC catalyst composition extends the entirelength of the substrate and the LTNA catalyst composition overlays aportion of the DOC composition.

In other embodiments, the DOC catalytic article comprises a layered DOCcatalyst composition and LTNA catalyst composition, and wherein the DOCcatalyst composition extends the entire length of the substrate and theDOC composition overlays the LTNA composition.

In still further embodiments, the DOC catalytic article comprises acombination of a zoned DOC catalyst composition and LTNA catalystcomposition and a layered DOC catalyst composition and LTNA catalystcomposition, and wherein the DOC catalyst composition extends the entirelength of the substrate and the DOC composition overlays a portion ofthe LTNA composition.

In yet further embodiments, the DOC catalytic article comprises alayered DOC catalyst composition and LTNA catalyst composition, andwherein the DOC catalyst composition extends the entire length of thesubstrate and the LTNA composition overlays the DOC composition.

In certain embodiments, the H₂-SCR catalytic article comprises a zonedH₂-SCR catalyst composition and LTNA catalyst composition located on anupstream and downstream zone, and wherein the upstream and thedownstream zones are adjacent and do not overlay each other.

In certain embodiments, the DOC catalytic article comprises a zoned DOCcatalyst composition and LTNA catalyst composition located on anupstream and downstream zone, and wherein the upstream and thedownstream zones are adjacent and do not overlay each other.

The order of the various components may vary and is not to be construedas limiting. It is understood, however, that a hydrogen injectionproduced from a hydrogen generator will be positioned upstream from theH₂-SCR catalytic article and in fluid communication with the H₂-SCRcatalytic article. It is also understood, that SCR catalysts operate inthe presence of a reductant, for example, ammonia or urea, and that thisreductant will be injected upstream from the corresponding SCR articleand in fluid communication with the corresponding SCR article (seereductant injection 140, 240, and 340 in FIGS. 1, 2, and 3 ,respectively).

It is also believed that positioning the H₂-SCR article prior to the LNTarticle or prior to the DOC article will provide optimal performance,particularly during cold start operations. The H₂-SCR article may beoperational at lower temperature, observed during cold start operations.The H₂-SCR article may generate heat during its operation, therebyraising the temperature of the exhaust gas to values that would improvethe operations of the LNT and DOC catalytic articles. In someembodiments, the H₂-SCR catalytic article may be positioned prior andimmediately adjacent to the LNT or DOC catalytic articles.Alternatively, there may be one or more additional articles (bricks)positioned between the H₂-SCR catalytic article and the LNT or DOCcatalytic articles.

In some embodiments, the H₂-SCR article, whether combined with a DOC ornot, may be placed in close coupled position located near the engine'sexhaust outlet or exhaust manifold, for example, within about 12 inchesof the exhaust outlet or exhaust manifold outlet. Alternatively, theH₂-SCR catalytic article may be positioned further downstream from theengine's exhaust outlet or exhaust manifold.

As used herein, the term “substrate” refers to the monolithic materialonto which a catalyst material (such as the H₂-SCR catalyst compositionor other catalyst compositions described herein) is placed, typically inthe form of a washcoat. A washcoat is formed by preparing a slurrycontaining a specified solids content (e.g., 30-90% by weight) ofcatalyst in a liquid, which is then coated onto a substrate and dried toprovide a washcoat layer. As used herein, the term “washcoat” has itsusual meaning in the art of a thin, adherent coating of a catalytic orother material applied to a substrate material, such as a honeycomb-typecarrier member, which is sufficiently porous to permit the passage ofthe gas stream being treated. The washcoat can optionally comprise abinder selected from silica, alumina, titania, zirconia, ceria, or acombination thereof. The loading of the binder is typically about 0.1 to10 wt. % based on the weight of the washcoat.

In one or more embodiments, the substrate is selected from one or moreof a flow-through honeycomb monolith or a particulate filter, and thecatalytic material(s) are applied to the substrate as a washcoat. FIGS.14A and 14B illustrate an exemplary substrate 2 in the form of aflow-through substrate coated with a catalyst composition as describedherein. Referring to FIG. 14A, the exemplary substrate 2 has acylindrical shape and a cylindrical outer surface 4, an upstream endface 6 and a corresponding downstream end face 8, which is identical toend face 6. Substrate 2 has a plurality of fine, parallel gas flowpassages 10 formed therein. As seen in FIG. 14B, flow passages 10 areformed by walls 12 and extend through carrier 2 from upstream end face 6to downstream end face 8, the passages 10 being unobstructed so as topermit the flow of a fluid, e.g., a gas stream, longitudinally throughcarrier 2 via gas flow passages 10 thereof. As more easily seen in FIG.14B, walls 12 are so dimensioned and configured that gas flow passages10 have a substantially regular polygonal shape. As shown, the catalystcomposition can be applied in multiple, distinct layers if desired. Inthe illustrated embodiment, the catalyst composition consists of both adiscrete bottom layer 14 adhered to the walls 12 of the carrier memberand a second discrete top layer 16 coated over the bottom layer 14. Thepresent invention can be practiced with one or more (e.g., 2, 3, or 4)catalyst layers and is not limited to the two-layer embodimentillustrated in FIG. 14B.

In one or more embodiments, the substrate is a ceramic or metal having ahoneycomb structure. Any suitable substrate may be employed, such as amonolithic substrate of the type having fine, parallel gas flow passagesextending there through from an inlet or an outlet face of the substratesuch that passages are open to fluid flow there through. The passages,which are essentially straight paths from their fluid inlet to theirfluid outlet, are defined by walls on which the catalytic material iscoated as a washcoat so that the gases flowing through the passagescontact the catalytic material. The flow passages of the monolithicsubstrate are thin-walled channels, which can be of any suitablecross-sectional shape and size such as trapezoidal, rectangular, square,sinusoidal, hexagonal, oval, circular, etc. Such structures may containfrom about 60 to about 900 or more gas inlet openings (i.e., cells) persquare inch of cross section.

A ceramic substrate may be made of any suitable refractory material,e.g., cordierite, cordierite-α-alumina, silicon nitride, zircon mullite,spodumene, alumina-silica-magnesia, zircon silicate, sillimanite, amagnesium silicate, zircon, petalite, α-alumina, an aluminosilicate andthe like. Substrates useful for the catalyst of embodiments of thepresent invention may also be metallic in nature and be composed of oneor more metals or metal alloys. A metallic substrate may include anymetallic substrate, such as those with openings or “punch-outs” in thechannel walls. Metallic substrates may be employed in various shapessuch as pellets, corrugated sheet or monolithic form. Specific examplesof metallic substrates include the heat-resistant, base-metal alloys,especially those in which iron is a substantial or major component. Suchalloys may contain one or more of nickel, chromium, and aluminum, andthe total of these metals may advantageously comprise at least about 15wt. % of the alloy, for instance, about 10 to 25 wt. % chromium, about 1to 8 wt. % of aluminum, and about 0 to 20 wt. % of nickel, in each casebased on the weight of the substrate.

In one or more embodiments, the substrate is a particulate filter. Asused herein, the terms “particulate filter” or “soot filter” refer to afilter designed to remove particulate matter from an exhaust gas streamsuch as soot. Particulate filters include, but are not limited tohoneycomb wall flow filters, partial filtration filters, wire meshfilters, wound fiber filters, sintered metal filters, and foam filters.

In certain embodiments, wall flow substrates used herein have aplurality of fine, substantially parallel gas flow passages extendingalong the longitudinal axis of the substrate. Typically, each passage isblocked at one end of the substrate body, with alternate passagesblocked at opposite end-faces. Such monolithic substrates may contain upto about 900 or more flow passages (or “cells”) per square inch of crosssection, although far fewer may be used. For example, the substrate mayhave from about 7 to 600, more usually from about 100 to 400, cells persquare inch (“cpsi”). The porous wall flow filter used in embodiments ofthe invention can be catalyzed in that the wall of said element hasthereon or contained therein a platinum group metal. Catalytic materialsmay be present on the inlet side of the substrate wall alone, the outletside alone, both the inlet and outlet sides, or the wall itself mayconsist all, or in part, of the catalytic material. In anotherembodiment, this invention may include the use of one or more catalystlayers and combinations of one or more catalyst layers on the inletand/or outlet walls of the substrate.

As seen in FIG. 15 , an exemplary wall flow substrate has a plurality ofpassages 52. The passages are enclosed by the internal walls 53 of thefilter substrate. The substrate has an inlet end 54 and an outlet end56. Alternate passages are plugged at the inlet end with inlet plugs 58,and at the outlet end with outlet plugs 60 to form opposing checkerboardpatterns at the inlet 54 and outlet 56. A gas stream 62 enters throughthe unplugged channel inlet 64, is stopped by outlet plug 60 anddiffuses through channel walls 53 (which are porous) to the outlet side66. The gas cannot pass back to the inlet side of walls because of inletplugs 58. The porous wall flow filter used in the invention can becatalyzed in that the wall of the substrate has thereon one or morecatalytic materials.

H₂-SCR Catalyst Compositions

Suitable H₂-SCR catalyst compositions may be formed on a ceramic ormetallic substrate upon which one or more catalyst coating compositionsmay be deposited. The substrate may comprise a flow through monolith ora porous wall flow filter as discussed in further detail herein. Theceramic substrate may be made of any suitable refractory material, e.g.,cordierite, cordierite-alumina, silicon nitride, zircon mullite,spodumene, alumina-silica magnesia, zircon silicate, sillimanite, amagnesium silicate, zircon, petalite, alumina, an aluminosilicate andthe like. The metallic substrates may be composed of one or more metalsor metal alloys. The metallic substrates may be employed in variousshapes such as corrugated sheet or monolithic form. Metals used formetallic substrates include the heat resistant metals and metal alloyssuch as titanium and stainless steel as well as other alloys in whichiron is a substantial or major component. Such alloys may contain one ormore of nickel, chromium and/or aluminum. The alloys may also containsmall or trace amounts of one or more other metals such as manganese,copper, vanadium, titanium and the like.

The catalyst coating composition deposited on the substrate of a H₂-SCRarticle may include one or more PGM components or another catalyticmetal such as Au or Ag. The PGM may be selected from the groupconsisting of Pd, Pt, Rh, Ir, Ru, Os, and combinations thereof. In someembodiments, the coating may comprise platinum, palladium, or acombination thereof. For instance, the platinum to palladium weightratio may range from about 1:10 to about 10:1, from about 1:5 to about10:1, from about 1:1 to about 10:1, from about 2:1 to about 10:1, orfrom about 3:1 to about 5:1. An exemplary PGM loading for the H₂-SCRcatalytic article is about 1 to about 200 g/ft³, such as about 10 toabout 50 g/ft³.

The catalyst coating composition may further comprise a support for thePGM component or components. Each PGM component can be supported on thesame or a different support. Each supported PGM catalyst can be preparedseparately or multiple PGM components can be impregnated in the sameprocess on the same support.

The support may be zeolitic or non-zeolitic. Examples of non-zeoliticsupports include, but are not limited to, high surface area refractorymetal oxides. High surface area refractory metal oxide supports cancomprise an activated compound selected from the group consisting ofalumina, zirconia, silica, titania, magnesia, ceria, lanthana, baria,tungsten oxide, and combinations thereof. Exemplary combinations includetitania-zirconia, zirconia-tungsten oxide, titania-tungsten oxide,silica-alumina, and magnesia-ceria. Examples of zeolitic supportsinclude, but are not limited to, small pore molecular sieves having theframework type of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO,CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI,MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SFW, SIV, THO, TSC,UEI, UFI, VNI, YUG, and ZON, medium pore molecular sieve having theFramework Type of MFI, FER, MWW, or EUO, large pore molecular sievehaving the Framework Type of CON, BEA, FAU, MOR, or EMT, as well asmixtures thereof. The hydrogen form of the zeolite is advantageous incertain embodiments, which can be prepared by ion exchange with hydrogenaccording to techniques known in the art. Examples of hydrogen formzeolites include H—Y, H-Beta, H-ZSM-5, H-Chabazite, H-Ferrierite,H-Mordenite, and the like.

The coating may be present at a concentration from about 10 g/ft³, about20 g/ft³, about 30 g/ft³, about 40 g/ft³, about 50 g/ft³ or about 60g/ft³ to about 100 g/ft³, about 150 g/ft³, about 200 g/ft³ or about 250g/ft³, based on the substrate. In some embodiments, the coating may beuniform. Alternatively, the substrate may be zone coated and/or layercoated.

LTNA Catalyst Compositions

Suitable LTNA compositions may be selected to allow for low temperatureNOx adsorption and storage while releasing the adsorbed NOx compoundsduring continuous lean operations, without the need for an activeregeneration (rich phase) step. The LTNA composition would preferably beable to withstand temperatures as high as about 800° C., be robust tosulfur poisoning, be able to release sulfur and recover NOx storagecapacity under lean conditions, and be cost effective by optimizing thePGM loading and PGM type.

In some embodiments, the LTNA may be coated on a substrate such as aflow through monolith or a porous wall flow filter, which may be eitherceramic or metallic. Ceramic substrates may be selected from the groupconsisting of alumina, silica, titania, ceria, zirconia, magnesia,zeolites, silicon nitride, silicon carbide, zirconium silicates,magnesium, silicates, aluminosilicates, metallo aluminosilicates (suchas cordierite and spudomene), or a mixture or mixed oxide of any two ormore thereof. Metallic substrates may be made of any suitable metal, andin particular heat-resistant metals and metal alloys such as titaniumand stainless steel as well as ferritic alloys containing iron, nickel,chromium, and/or aluminum in addition to other trace metals.

The LTNA composition may further comprise a support comprising extensivethree dimensional networks such as molecular sieves. The molecularsieves may be small pore molecular sieves having the framework type ofACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT,EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI,OWE, PAU, PHI, RHO, RTH, SAT, SAV, SFW, SIV, THO, TSC, UEI, UFI, VNI,YUG, and ZON, medium pore molecular sieve having the Framework Type ofMFI, FER, MWW, or EUO, large pore molecular sieve having the FrameworkType of CON, BEA, FAU, MOR, or EMT, as well as mixtures thereof.

The LTNA may further comprise PGM selected from the group consisting ofPd, Pt, Rh, Au, Ag, Ir, Ru, Os, and combinations thereof. The loading ofthe PGM may be in the range of about 10 g/ft³ to about 250 g/ft³, forexample from about 20 g/ft³, about 30 g/ft³, about 40 g/ft³, about 50g/ft³ or about 60 g/ft³ to about 100 g/ft³, about 150 g/ft³ or about 200g/ft³, based on the substrate.

LNT Catalyst Compositions

Suitable LNT catalyst compositions comprise a NOx sorbent and a support,for instance a NOx sorbent and a platinum group metal componentdispersed on a refractory metal oxide support. The LNT catalystcomposition may optionally contain other components such as oxygenstorage components. The LNT catalyst composition may be in the form of asingle layer or a multi-layer coating. For instance, a bi-layer catalystcoating with a bottom layer adhered to the substrate and the top layeroverlying and in contact with a portion of or the entire bottom layer.

A suitable NOx sorbent comprises a basic oxygenated compound of analkaline earth element selected from magnesium, calcium, strontium,barium and mixtures thereof and an oxygenated compound of a rare earthcomprising cerium (ceria component). The rare earth may further containone or more of lanthanum, neodymium or praseodymium.

The NOx sorbent component may be present for instance in a concentrationof from about 0.1 to about 4.0 g/in³, for example from about 0.2 g/in³,about 0.3 g/in³, about 0.4 g/in³, about 0.5 g/in³, about 0.6 g/in³,about 0.7 g/in³ or about 0.8 g/in³ to about 1.0 g/in³, about 1.5 g/in³,about 2.0 g/in³, about 2.5 g/in³, about 3.0 g/in³ or about 3.5 g/in³,based on the substrate.

Platinum group metal components promote oxidation and reduction ofnitrogen species. The loading of the platinum group metal component maybe in the range of about 10 g/ft³ to about 250 g/ft³, for example fromabout 20 g/ft³, about 30 g/ft³, about 40 g/ft³, about 50 g/ft³ or about60 g/ft³ to about 100 g/ft³, about 150 g/ft³ or about 200 g/ft³, basedon the substrate. If more than one coating layers are present, aplatinum group metal component in different layers may be identical ordifferent. Likewise, the amounts of platinum group metal components indifferent layers may be identical or different.

The support comprises at least a high surface area refractory metaloxide such as alumina, titania, zirconia; mixtures of alumina with oneor more of titania, zirconia, silica, chromia, and ceria; ceria coatedon alumina or titania coated on alumina. The refractory metal oxide mayhave a specific surface area of about 50 m²/g to about 300 m²/g and maybe present for instance in a concentration of from about 1.5 g/in³ toabout 7.0 g/in³, based on the substrate.

DOC Catalyst Compositions

Suitable DOC catalysts may be formed on a ceramic or metallic substrateupon which one or more catalyst coating compositions may be deposited.Suitable DOC substrates may include a ceramic or metal honeycombstructure.

The DOC substrate may be a monolith having fine, parallel gas flowpassages extending therethrough from an inlet or an outlet of thesubstrate, such that passages are open to fluid flow therethrough(referred to herein as flow-through substrates). The passages, which areessentially straight paths from their fluid inlet to their fluid outlet,are defined by walls on which the catalytic material is coated as awashcoat so that the gases flowing through the passages contact thecatalytic material. The flow passages of the monolithic substrate arethin-walled channels, which can be of any suitable cross-sectional shapeand size such as trapezoidal, rectangular, square, sinusoidal,hexagonal, oval, circular, etc. Such monolithic carriers may contain upto about 1200 or more flow passages (or “cells”) per square inch ofcross section, although far fewer may be used. Flow-through substratestypically have a wall thickness between 0.002 and 0.1 inches.

The ceramic substrate may be made of any suitable refractory material,e.g., cordierite, cordierite-alumina, silicon nitride, zircon mullite,spodumene, alumina-silica magnesia, zircon silicate, sillimanite, amagnesium silicate, zircon, petalite, alumina, an aluminosilicate andthe like.

The metallic substrates may be composed of one or more metals or metalalloys. The metallic substrates may be employed in various shapes suchas corrugated sheet or monolithic form. Metals used for metallicsubstrates include the heat resistant metals and metal alloys such astitanium and stainless steel as well as other alloys in which iron is asubstantial or major component. Such alloys may contain one or more ofnickel, chromium and/or aluminum. The alloys may also contain small ortrace amounts of one or more other metals such as manganese, copper,vanadium, titanium and the like.

The catalyst coating composition deposited on the substrate of a DOCarticle may include one or more layers of platinum group metals thatpromote oxidation of noxious compounds. In some embodiments, the coatingmay comprise platinum, palladium, or a combination thereof. Forinstance, the platinum to palladium weight ratio may range from about1:10 to about 10:1, from about 1:5 to about 10:1, from about 1:1 toabout 10:1, from about 2:1 to about 10:1, or from about 3:1 to about5:1. The coating may be present at a concentration from about 10 g/ft³,about 20 g/ft³, about 30 g/ft³, about 40 g/ft³, about 50 g/ft³ or about60 g/ft³ to about 100 g/ft³, about 150 g/ft³, about 200 g/ft³ or about250 g/ft³, based on the substrate. In some embodiments, the coating maybe uniform. Alternatively, the substrate may be zone coated.

SCR Catalyst Compositions

SCR compositions may be employed in catalytic articles used exclusivelyfor SCR as well as for zoned catalytic articles used, for instance, forH₂-SCR, SCR with AMOX, etc. Suitable SCR compositions may be in the formof a catalytic coating comprising one or more coating layers and may bedisposed at least on a portion of a substrate. SCR catalysts includebase metal (e.g., copper and/or iron) ion-exchanged molecular sieves.

Present molecular sieves for instance have 8-ring pore openings anddouble-six ring secondary building units, for example, those having thefollowing structure types: AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS,SAT or SAV. In one or more embodiments, the 8-ring small pore molecularsieve has the CHA crystal structure.

The molecular sieves may have a silica to alumina ratio (SAR) of fromabout 2, about 5, about 8, about 10, about 15, about 20 or about 25 toabout 30, about 35, about 40, about 45, about 50, about 60, about 70,about 80 about 90, about 100, about 150, about 200, about 260, about300, about 400, about 500, about 750 or about 1000.

In some embodiments, the molecular sieves may have a SAR of from about 2to about 300, from about 5 to about 250, from about 10 to about 250,from about 15 to about 250, from about 10 to about 200, from about 10 toabout 100, from about 10 to about 75, from about 10 to about 60, fromabout 10 to about 50, from about 15 to about 100, from about 15 to about75, from about 15 to about 60, from about 15 to about 50, from about 20to about 100, from about 20 to about 75, from about 20 to about 60 orfrom about 20 to about 50.

For example the amount of copper in the molecular sieve may be about0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8,about 0.9, about 1.0, about 1.1, about 1.2, about 1.3, about 1.4, about1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0 wt %, about2.1, about 2.2, about 2.3, about 2.4, about 2.5, about 2.6, about 2.7,about 2.8, about 2.9, about 3.0, about 3.1, about 3.2, about 3.3, about3.4, about 3.5, about 3.6, about 3.7, about 3.8, about 3.9, about 4.0,about 4.1, about 4.2, about 4.3, about 4.4, about 4.5, about 4.6, about4.7, about 4.8, about 4.9, about 5.0 wt %, or about 10.0 wt %, based onthe total weight of a copper-containing molecular sieve.

For example, the amount of iron in the iron-containing molecular sieveis about 1.0, about 3.0, about 3.5, about 4.0, about 4.5, about 5.0,about 5.5, about 6.0, about 6.5, about 7.0, about 7.5, about 8.0, about8.5, about 9.0, about 9.5, about 10 wt %, or about 15 wt %, based on thetotal weight of the molecular sieve.

Amounts of catalytic metals like copper or iron in a molecular sieve arereported as the oxide, CuO or Fe₂O₃.

The copper- or iron-containing molecular sieves may exhibit a BETsurface area, determined according to DIN 66131, of at least about 400m²/g, at least about 550 m²/g or at least about 650 m²/g, for examplefrom about 400 to about 750 m²/g or from about 500 to about 750 m²/g.The molecular sieves may have a mean crystal size of from about 10nanometers to about 10 microns, from about 50 nanometers to about 5microns or from about 0.1 microns to about 0.5 microns as determined viaSEM.

Molecular sieves refer to materials having an extensivethree-dimensional network of oxygen ions containing generallytetrahedral type sites and having a pore distribution of relativelyuniform pore size. A zeolite is a specific example of a molecular sieve,further including silicon and aluminum. Reference to a“non-zeolite-support” or “non-zeolitic support” in a catalyst layerrefers to a material that is not a zeolite and that receives preciousmetals, stabilizers, promoters, binders and the like throughassociation, dispersion, impregnation or other suitable methods.Examples of such non-zeolitic supports include, but are not limited to,high surface area refractory metal oxides. A non-limiting example of anSCR catalyst with a non-zeolitic support may be the vanadium titaniumcatalyst.

When present on a substrate, for example a honeycomb monolith substrate,SCR catalyst compositions are present at a concentration of for instancefrom about 0.3 to 4.5 g/in³, or from about 0.4, about 0.5, about 0.6,about 0.7, about 0.8, about 0.9 or about 1.0 g/in³ to about 1.5 g/in³,about 2.0 g/in³, about 2.5 g/in³, about 3.0 g/in³, about 3.5 g/in³ orabout 4.0 g/in³, based on the substrate.

AMOX Catalyst Compositions

AMOX catalysts are taught, for instance, in U.S. Pub. No. 2011/0271664.An ammonia oxidation (AMOX) catalyst may be a supported precious metalcomponent which is effective to remove ammonia from an exhaust gasstream. The precious metal may include ruthenium, rhodium, iridium,palladium, platinum, silver or gold. For example, the precious metalcomponent includes physical mixtures or chemical or atomically-dopedcombinations of precious metals. The precious metal component, forinstance, includes platinum. Platinum may be present in an amount offrom about 0.008% to about 2 wt % based on the AMOX catalyst.

The precious metal component (such as a PGM component) is typicallydeposited on a high surface area refractory metal oxide support.Examples of suitable high surface area refractory metal oxides includealumina, silica, titania, ceria, and zirconia, as well as physicalmixtures, chemical combinations and/or atomically-doped combinationsthereof. In specific embodiments, the refractory metal oxide may containa mixed oxide such as silica-alumina, amorphous or crystallinealuminosilicates, alumina-zirconia, alumina-lanthana, alumina-baria,alumina-ceria and the like. An exemplary refractory metal oxidecomprises high surface area γ-alumina having a specific surface area ofabout 50 to about 300 m²/g.

The AMOX catalyst may include a zeolitic or non-zeolitic molecularsieve, for example, selected from those of the CHA, FAU, BEA, MFI andMOR types. A molecular sieve may be physically mixed with anoxide-supported platinum component. In an alternative embodiment,platinum may be distributed on the external surface or in the channels,cavities or cages of the molecular sieve.

CSF Compositions

The catalyzed soot filter may comprise a “flow-through” substrate as theones described herein and may have a catalytic coating disposed thereon.Alternatively, the soot filter may comprise a wall-flow filter substratemade from materials such as cordierite, aluminum titanate, or siliconcarbide. Loading of the catalytic coating on a wall-flow substrate willdepend on substrate properties such as porosity and wall thickness andtypically will be lower than the catalyst loading on a flow-throughsubstrate. The type of catalytic coating on the CSF can vary, and caninclude an oxidation catalyst composition and/or an SCR catalystcomposition.

Wall-flow filter substrates, as discussed herein, may have a pluralityof fine, substantially parallel gas flow passages extending along thelongitudinal axis of the substrate. Typically, each passage is blockedat one end of the substrate body, with alternate passages blocked atopposite end-faces. Such monolithic carriers may contain up to about 700or more flow passages (or “cells”) per square inch of cross-section,although far fewer may be used. The cells can have cross-sections thatare rectangular, square, circular, oval, triangular, hexagonal, or areof other polygonal shapes. Wall-flow substrates typically have a wallthickness from about 50 microns to about 2000 microns. Wall-flow filterswill generally have a wall porosity of at least 50% with an average poresize of at least 5 microns prior to disposition of the catalyticcoating.

In the present systems, the H₂-SCR substrate and/or DOC substrate and/orLNT substrate and/or H₂-SCR/DOC combined catalytic article substrateand/or SCR substrate and/or AMOX substrate and/or SCR/AMOX combinedcatalytic article substrate may each independently be selected from thegroup consisting of a flow-through monolith and a porous wall-flowsubstrate.

Methods for Treating Streams Containing NOx

In some embodiments, the present disclosure is directed to a method fortreating an exhaust stream containing NOx, comprising passing theexhaust stream through the emission treatment systems or throughcatalytic articles disclosed herein.

Present methods include treating exhaust gas stream during a cold phase,or cold start phase, that is where the exhaust gas temperatures areabout 200° C. or lower, about 175° C. or lower, about 150° C. or lower,about 125° C. or lower, or about 100° C. or lower.

Present articles, systems and methods are suitable for treatment ofexhaust gas streams from mobile emissions sources. Articles, systems andmethods are also suitable for treatment of exhaust streams fromstationary sources such as power plants.

EXPERIMENTAL

Various catalyst compositions comprising one or more PGM metalssupported on a metal oxide or zeolite support were prepared and testedfor H₂-SCR reaction activity.

Sample Preparation

Method 1 (Single Metal Catalysts):

For Pt catalysts, a Pt amine hydroxide solution was impregnated onto acommercially available catalyst support using the incipient wetnesstechnique to achieve a desirable metal loading. For Pd, Ru, Rh and Ircatalysts, the corresponding nitrate solutions were used for theimpregnation. The impregnated support was then calcined at 500° C. for 2hours in air. To shape the sample for reactor test, the calcined powderwas dispersed in deionized water at about 30% solid content, and in thisslurry an alumina binder (5% of the catalyst) was added. This slurry wascontinuously stirred until dry. The dried powder was further calcined at450° C. for 2 hours in air and then crushed and sieved to 250-500 μmfraction. Before reactor testing, the sieved fraction was aged at 750°C. for 20 hours with 10% steam in air.

Method 2 (Pt/Pd Catalysts):

For Pt/Pd bimetallic catalysts, Pd nitrate solution was firstimpregnated on a support powder to achieve 100% incipient wetness. ThisPd impregnated powder was dried at 100° C. before Pt impregnation. Ptwas then impregnated on this Pd/support powder using the method similarto Method 1 and dried at 100° C. The Pt/Pd powder was then calcined at450° C. for 2 hours in air. The sample shaping method and agingconditions are the same as described in Method 1.

Method 3 (PGM on TiO₂—ZrO₂):

The method is the same as Method 1. However, the support material wasmade in the lab following a procedure described by Machida et al. [M.Machida, S. Ikeda, D. Kurogi and T. Kijima, Appl. Catal. B 35 (2001)107-116.] TiO₂—ZrO₂ (1:1) was prepared by co-precipitating Ti(OPr)₄ andZrO(NO₃)₂ mixtures with NH₄OH solution. The precipitated solution wasthen evaporated to dryness. The resulting solid product was calcined at450° C. in air. The sample shaping method and aging conditions are thesame as described in Method 1.

Method 4 (PGM on MgO—CeO₂):

The method is the same as Method 1. However, the support material wasmade in the lab following a procedure described by Costa et al. [C. N.Costa, P. G. Savva, J. L. Fierro, A. M. Efstathiou, Appl. Catal. B 75(2007) 147-156. [2] EP 2269729 A1.] The MgO—CeO₂ support (1:1) wasprepared by the sol-gel method using Mg(EtO)₂ and Ce(NO₃)₃ asprecursors. The resulting solid was calcined at 600° C. for 4 hours inair. The Pt and Pd impregnation was conducted using the same methoddescribed in Method 1. The sample shaping method and aging conditionsare the same as described in Method 1.

Method 5 (PGM on Sulfated MgO—CeO₂):

Same as Method 4, except a sulfation treatment was conducted before PGMimpregnation. The MgO—CeO2 support was treated with 20 ppm SO₂/air at300° C. for 20 hours. The sample shaping method and aging conditions arethe same as described in Method 1.

Method 6 (PGM on WO₃/ZrO₂):

The support material, WO₃/ZrO₂ (10% WO₃), was made in lab byimpregnating (NH₄)₆H₂W₁₂O₄₁ solution onto a commercially available ZrO₂support using the incipient wetness technique. The resulting powder wasdried overnight at 110° C. for 2 hours in air and calcined at 500° C.for 2 hours before impregnating Pt or Pd. The sample shaping method andaging conditions are the same as described in Method 1.

Method 7 (Pd/(Al₂O₃++ZSM-5)+TiO₂):

Pd/(Al₂O₃+ZSM-5)+TiO₂ catalyst was prepared by impregnating Pd nitrateon a mixture of Al₂O₃ and ZSM-5 zeolite (3:1 by weight) using theprocedure described in Method 1. To this Pd/(Al₂O₃+ZSM-5) material, TiO₂was added (20% TiO₂ by weight). The mixture was calcined at 500° C. for2 hours in air. The sample shaping method and aging conditions are thesame as described in Method 1.

Reactor Test Conditions

The H₂-SCR reaction was tested with a high-throughput reactor capable oftesting 48 samples in a single test run. The activity was measured atconstant temperatures at 100, 125, 150, 175 and 200, 250 and 350° C. Foreach run, 0.2 g of sample was used with a flow rate of 50 L/min, whichis equivalent a monolithic GHSV of 30,000 h⁻¹ with 2 g/in³ washcoatloading. Several reaction feeds were used for activity measurement. Thepercentages noted below in the feed descriptions are by volume.

Feed 1: 200 ppm NO, 5% O₂, 5% H₂O, variable H₂ and balance N₂. H₂concentration: 0.2, 0.4, 0.6, 0.8 and 1%.

Feed 2: 500 ppm CO, 200 ppm NO, 5% O₂, 5% H₂O, 1% H₂ and balance N₂.

Feed 3: 100 ppm C₃H₆, 200 ppm NO, 5% O₂, 5% H₂O, 1% H₂ and balance N₂.

Examples 1-1 to 1-37

A series of single metal catalysts were prepared using the samplepreparation methods noted above. These catalysts were designated 1-1through 1-37 and are set forth in Table 1 below, with the metal loading,support, presence of an additive, and the sample preparation methodnoted therein.

TABLE 1 List of single metal catalysts* Sample Preparation ID SampleName Metal Support Additive method 1-1 1% Pt/Al₂O₃ 1% Pt Al₂O₃ 1 1-2 1%Pt/SiO₂ 1% Pt SiO₂ 1 1-3 1% Pt/CeO₂ 1% Pt CeO₂ 1 1-4 1% Pt/TiO₂ 1% PtTiO₂ 1 1-5 1% Pt/ZrO₂ 1% Pt ZrO₂ 1 1-6 1% Pt/TiO2—ZrO2 1% Pt TiO2—ZrO2 31-7 1% Pt/WO₃/ZrO₂ 1% Pt WO₃/ZrO₂ 6 1-8 1% Pt/WO₃/TiO₂ 1% Pt WO₃/TiO₂ 11-9 1% Pt/SiO₂/Al₂O₃ 1% Pt SiO₂/Al₂O₃ 1 1-10 1% Pt/MgO 1% Pt MgO 1 1-111% Pt/MgO—CeO₂ 1% Pt MgO—CeO₂ 4 1-12 0.1% Pt/MgO—CeO₂ (A) 0.1% Pt  MgO—CeO₂ 4 1-13 0.1% Pt/MgO—CeO₂ (B) 0.1% Pt   MgO—CeO₂ 5 1-14 1% Pt/H—Y1% Pt H—Y 1 1-15 1% Pt/H-ZSM-5 1% Pt H-ZSM-5 1 1-16 1% Pt/H-Beta 1% PtH-Beta 1 1-17 1% Pt/H-Chabazite 1% Pt H-Chabazite 1 1-18 1% PdAl₂O₃ 1%Pd Al₂O₃ 1 1-19 1% Pd/SiO₂ 1% Pd SiO₂ 1 1-20 1% Pd/CeO₂ 1% Pd CeO₂ 11-21 1% Pd/TiO₂ 1% Pd TiO₂ 1 1-22 1% Pd/ZrO₂ 1% Pd ZrO₂ 1 1-23 1%Pd/TiO2—ZrO2 1% Pd TiO2—ZrO2 3 1-24 1% Pd/WO₃/ZrO₂ 1% Pd WO₃/ZrO₂ 6 1-251% Pd/WO₃/TiO₂ 1% Pd WO₃/TiO₂ 1 1-26 1% Pd/SiO₂/Al₂O₃ 1% Pd SiO₂/Al₂O₃ 11-27 1% Pd/MgO 1% Pd MgO 1 1-28 1% Pd/MgO—CeO₂ 1% Pd MgO—CeO₂ 4 1-29 1 %Pd/H—Y 1% Pd H—Y 1 1-30 1% Pd/H-ZSM-5 1% Pd H-ZSM-5 1 1-31 1% Pd/H-Beta1% Pd H-Beta 1 1-32 1% PdH-Chabazite 1% Pd H-Chabazite 1 1-33 1%Pd/(Al₂O₃ + ZSM-5) + TiO₂ 1% Pd Al₂O₃ + ZSM-5 TiO₂ 7 1-34 0.2%Pd/(Al₂O₃ + ZSM-5) + TiO₂ 0.2% Pd   Al₂O₃ + ZSM-5 TiO₂ 7 1-35 1%Rh/Al₂O₃ 1% Rh Al₂O₃ 1 1-36 1% Ru/Al₂O₃ 1% Ru Al₂O₃ 1 1-37 1% Ir/Al₂O₃1% Ir Al₂O₃ 1 *Metal % is based on weight.

Examples 2-1 to 2-47

A further series of single metal and bimetallic catalysts were preparedusing the sample preparation methods noted above. These catalysts weredesignated 2-1 through 2-47 and are set forth in Table 2 below, with themetal loading and support shown. All of the single metal catalysts inTable 2 were made using Method 1 above and all the bimetallic catalystsin Table 2 were made using Method 2 above.

TABLE 2 List of Pt—Pd bimetallic catalysts* Sample ID Sample Name MetalSupport 2-1 Pt/Mg—Y Pt-only Mg—Y (Mg exchanged) 2-2 Pt/H—Y Pt-only H—Y2-3 Pt/Beta Pt-only H-Beta 2-4 Pt/H-CHA Pt-only H-Chabazite 2-5Pt/H-ZSM-5 Pt-only H-ZSM-5 2-6 Pt/H-MOR Pt-only H-Mordenite 2-7 Pt/H-FERPt-only H-Ferrierite 2-8 Pt/ZrO₂ Pt-only ZrO₂ 2-9 Pt/WO₃/TiO₂ Pt-onlyWO₃/TiO₂ 2-10 Pt/MgO Pt-only MgO 2-11 Pt/Mg—Al HT Pt-only Calcined Mg/Alhydrotalcite 2-12 Pt/Pd_8:1/H—Y Pt/Pd = 8:1 H—Y 2-13 Pt/Pd_8:1/H-BetaPt/Pd = 8:1 H-Beta 2-14 Pt/Pd_8:1/H-CHA Pt/Pd = 8:1 H-Chabazite 2-15Pt/Pd_8:1/H-ZSM-5 Pt/Pd = 8:1 H-ZSM-5 2-16 Pt/Pd_8:1/H-MOR Pt/Pd = 8:1H-Mordenite 2-17 Pt/Pd_8:1/H-FER Pt/Pd = 8:1 H-Ferrierite 2-18Pt/Pd_8:1/ZrO₂ Pt/Pd = 8:1 ZrO₂ 2-19 Pt/Pd_8:1/WO₃/TiO₂ Pt/Pd = 8:1WO₃/TiO₂ 2-20 Pt/Pd_4:1/H—Y Pt/Pd = 4:1 H—Y 2-21 Pt/Pd_4:1/H-Beta Pt/Pd= 4:1 H-Beta 2-22 Pt/Pd_4:1/H-CHA Pt/Pd = 4:1 H-Chabazite 2-23Pt/Pd_4:1/H-ZSM-5 Pt/Pd = 4:1 H-ZSM-5 2-24 Pt/Pd_4:1/H-MOR Pt/Pd = 4:1H-Mordenite 2-25 Pt/Pd_4:1/H-FER Pt/Pd = 4:1 H-Ferrierite 2-26Pt/Pd_4:1/ZrO₂ Pt/Pd = 4:1 ZrO₂ 2-27 Pt/Pd_4:1/WO₃/TiO₂ Pt/Pd = 4:1WO₃/TiO₂ 2-28 Pt/Pd_4:1/MgO Pt/Pd = 4:1 MgO 2-29 Pt/Pd_4:1/Mg—Al Pt/Pd =4:1 Calcined Mg/Al hydrotalcite 2-30 Pt/Pd_2:1/H—Y Pt/Pd = 2:1 H—Y 2-31Pt/Pd_2:1/H-Beta Pt/Pd = 2:1 H-Beta 2-32 Pt/Pd_2:1/H-CHA Pt/Pd = 2:1H-Chabazite 2-33 Pt/Pd_2:1/H-ZSM-5 Pt/Pd = 2:1 H-ZSM-5 2-34Pt/Pd_2:1/H-MOR Pt/Pd = 2:1 H-Mordenite 2-35 Pt/Pd_2:1/H-FER Pt/Pd = 2:1H-Ferrierite 2-36 Pt/Pd_2:1/ZrO₂ Pt/Pd = 2:1 ZrO₂ 2-37Pt/Pd_2:1/WO₃/TiO₂ Pt/Pd = 2:1 WO₃/TiO₂ 2-38 Pd/H—Y Pd-only H—Y 2-39Pd/Beta Pd-only H-Beta 2-40 Pd/H-CHA Pd-only H-Chabazite 2-41 Pd/H-ZSM-5Pd-only H-ZSM-5 2-42 Pt/H-MOR Pd-only H-Mordenite 2-43 Pd/H-FER Pd-onlyH-Ferrierite 2-44 Pd/ZrO₂ Pd-only ZrO₂ 2-45 Pd/WO₃/TiO₂ Pd-only WO₃/TiO₂2-46 Pd/MgO Pd-only MgO 2-47 Pd/Mg—Al Pd-only Calcined Mg/Alhydrotalcite *Total metal loading is 1% by weight; Pt/Pd is weightratio.

Table 3 below summarizes the NO_(x) conversion and N₂ yield (NO_(x)converted to N₂) of single metal catalysts 1-1 through 1-37 tested at125° C. with 0.4% H₂ in the feed gas. In general, Pt catalysts are moreactive (higher NO_(x) conversion) than the corresponding Pd catalysts.However, Pt catalysts normally also produce more N₂O (a byproduct). Thetop 10 catalysts for highest N₂ yield arePt/HY>Pd/HCHA˜Pt/HZSM-5˜Pt/ZrO₂>Pt/HCHA>Pt/TiO₂—ZrO₂>Pd/MgO>Pt/TiO₂˜Pd/TiO₂>Pd/HBeta.

TABLE 3 Performance of catalysts tested at 125° C. with 0.4% H₂ in feedNO_(x) N₂ Sample ID Sample Name Conversion (%) Yield (%) 1-1 1% Pt/Al₂O₃85 23 1-2 1% Pt/SiO₂ 100 23 1-3 1% Pt/CeO₂ 5 1 1-4 1% Pt/TiO₂ 93 30 1-51% Pt/ZrO₂ 93 57 1-6 1% Pt/TiO2—ZrO2 87 47 1-7 1% Pt/WO₃/ZrO₂ 65 34 1-81% Pt/WO₃/TiO₂ 68 19 1-9 1% Pt/SiO₂/Al₂O₃ 85 23 1-10 1% Pt/MgO 39 321-11 1% Pt/MgO—CeO₂ 9 4 1-12 0.1% Pt/MgO—CeO₂ (A) 7 3 1-13 0.1%Pt/MgO—CeO₂ (B) 3 0 1-14 1% Pt/H—Y 95 66 1-15 1% Pt/H-ZSM-5 96 57 1-161% Pt/H-Beta 35 21 1-17 1% Pt/H-CHA 92 54 1-18 1% PdAl₂O₃ 2 0 1-19 1%Pd/SiO₂ 10 2 1-20 1% Pd/CeO₂ 6 2 1-21 1% Pd/TiO₂ 37 30 1-22 1% Pd/ZrO₂ 00 1-23 1% Pd/TiO2—ZrO2 29 18 1-24 1% Pd/WO₃/ZrO₂ 24 21 1-25 1%Pd/WO₃/TiO₂ 26 17 1-26 1% Pd/SiO₂/Al₂O₃ 4 1 1-27 1% Pd/MgO 66 43 1-28 1%Pd/MgO—CeO₂ 33 18 1-29 1% Pd/H—Y 44 25 1-30 1% Pd/H-ZSM-5 28 17 1-31 1%Pd/H-Beta 42 26 1-32 1% PdH-CHA 68 58 1-33 1% Pd/(Al₂O₃ + 9 6 ZSM-5) +TiO₂ 1-34 0.2% Pd/(Al₂O₃ + 8 5 ZSM-5) + TiO₂ 1-35 1% Rh/Al₂O₃ 5 2 1-361% Ru/Al₂O₃ 4 1 1-37 1% Ir/Al₂O₃ 5 2

Table 4 below shows the NO_(x) conversions of catalysts 1-1 through 1-37tested at various temperatures with 1% H₂ in feed. The activity on mostof the catalyst is significantly increased with the increased H₂concentration. Even at 100° C., most of the catalysts show >90% NO_(x)conversion. The lowest activity was found on Rh, Ru and Ir catalysts aswell as on the Pt and Pd catalysts supported on materials containingCeO₂.

TABLE 4 NO_(x) conversion (%) of catalysts as a function of reactiontemperature at 1% H₂ Sample ID Sample Name 100° C. 125° C. 150° C. 175°C. 200° C. 1-1 1% Pt/Al₂O₃ 91 83 72 65 63 1-2 1% Pt/SiO₂ 99 96 90 86 841-3 1% Pt/CeO₂ 2 10 15 20 34 1-4 1% Pt/TiO₂ 99 96 89 82 78 1-5 1%Pt/ZrO₂ 71 92 92 87 78 1-6 1% Pt/TiO2—ZrO2 95 96 79 68 58 1-7 1%Pt/WO₃/ZrO₂ 83 82 75 65 57 1-8 1% Pt/WO₃/TiO₂ 90 88 82 73 65 1-9 1%Pt/SiO₂/Al₂O₃ 92 85 79 76 74 1-10 1% Pt/MgO 38 55 69 83 91 1-11 1%Pt/MgO—CeO₂ 4 16 22 28 45 1-12 0.1% Pt/MgO—CeO₂ (A) 4 15 21 25 38 1-130.1% Pt/MgO—CeO₂ (B) 0 9 13 18 25 1-14 1% Pt/H—Y 95 96 96 92 86 1-15 1%Pt/H-ZSM-5 99 100 90 81 73 1-16 1% Pt/H-Beta 20 69 100 99 99 1-17 1%Pt/H-CHA 97 91 81 74 68 1-18 1% PdAl₂O₃ 18 26 31 32 34 1-19 1% Pd/SiO₂41 35 47 48 62 1-20 1% Pd/CeO₂ 2 11 18 23 41 1-21 1% Pd/TiO₂ 97 96 97 9490 1-22 1% Pd/ZrO₂ 35 46 46 37 27 1-23 1% Pd/TiO2—ZrO2 86 88 87 79 701-24 1% Pd/WO₃/ZrO₂ 86 90 90 89 83 1-25 1% Pd/WO₃/TiO₂ 90 92 95 95 911-26 1% Pd/SiO₂/Al₂O₃ 28 46 50 45 48 1-27 1% Pd/MgO 92 99 96 93 87 1-281% Pd/MgO—CeO₂ 86 80 72 61 51 1-29 1% Pd/H—Y 90 90 89 87 81 1-30 1%Pd/H-ZSM-5 84 79 79 77 72 1-31 1% Pd/H-Beta 96 97 94 91 85 1-32 1%PdH-CHA 65 91 86 82 80 1-33 1% Pd/(Al₂O₃ + ZSM-5) + TiO₂ 58 72 78 78 781-34 0.2% Pd/ 66 71 84 87 87 (Al₂O₃ + ZSM-5) + TiO₂ 1-35 1% Rh/Al₂O₃ 213 17 23 38 1-36 1% Ru/A1₂O₃ 2 11 15 18 29 1-37 1% Ir/A1₂O₃ 1 11 14 1726

Table 5 below shows the NO_(x) conversion and N₂ yield for catalysts 2-1through 2-47 at 125° C. with 0.4% H₂. In general, the Pt/Pd catalystsbehave more like Pt catalysts in NO_(x) conversion and weakly dependenton Pt/Pd ratio. However, the N₂ yield is optimized at different Pt/Pdratio for different supports. For example, for H—Y supported catalysts,the highest N₂ yield (70%) was found at Pt/Pd=8:1, while WO₃/TiO₂supported catalysts show the highest N₂ yield (73%) at Pt/Pd=4:1. Mostof the Pt/Pd catalysts show much higher N₂ yield than the correspondingPd catalysts.

TABLE 5 Performance of catalysts tested at 125° C. with 0.4% H₂ in feedSample ID Sample Name NO_(x) Conversion (%) N₂ Yield (%) 2-1 Pt/Mg—Y 9861 2-2 Pt/H—Y 97 62 2-3 Pt/Beta 96 71 2-4 Pt/H-CHA 91 60 2-5 Pt/H-ZSM-593 51 2-6 Pt/H-MOR 93 52 2-7 Pt/H-FER 88 62 2-8 Pt/ZrO₂ 96 49 2-9Pt/WO₃/TiO₂ 95 38 2-10 Pt/MgO 3 2 2-11 Pt/Mg—Al HT 48 27 2-12Pt/Pd_8:1/H—Y 98 70 2-13 Pt/Pd_8:1/H-Beta 25 16 2-14 Pt/Pd_8:1/H-CHA 9352 2-15 Pt/Pd_8:1/H-ZSM-5 97 53 2-16 Pt/Pd_8:1/H-MOR 94 54 2-17Pt/Pd_8:1/H-FER 91 64 2-18 Pt/Pd_8:1/ZrO₂ 96 40 2-19 Pt/Pd_8:1/WO₃/TiO₂97 60 2-20 Pt/Pd_4:1/H—Y 98 69 2-21 Pt/Pd_4:1/H-Beta 12 7 2-22Pt/Pd_4:1/H-CHA 95 56 2-23 Pt/Pd_4:1/H-ZSM-5 97 58 2-24 Pt/Pd_4:1/H-MORNot tested Not tested 2-25 Pt/Pd_4:1/H-FER 87 61 2-26 Pt/Pd_4:1/ZrO₂ 9743 2-27 Pt/Pd_4:1/WO₃/TiO₂ 97 67 2-28 Pt/Pd_4:1/MgO 9 2 2-29 Pt/Pd_4:1/Mg—Al 56 40 2-30 Pt/Pd_2:1/H—Y 98 65 2-31 Pt/Pd_2:1/H-Beta 13 7 2-32Pt/Pd_2:1/H-CHA 94 55 2-33 Pt/Pd_2:1/H-ZSM-5 94 58 2-34 Pt/Pd_2:1/H-MOR90 55 2-35 Pt/Pd_2:1/H-FER 95 65 2-36 Pt/Pd_2:1/ZrO₂ 97 53 2-37Pt/Pd_2:1/WO₃/TiO₂ 93 73 2-38 Pd/H—Y 36 19 2-39 Pd/Beta 42 26 2-40Pd/H-CHA 68 58 2-41 Pd/H-ZSM-5 28 17 2-42 Pd/H-MOR 25 8 2-43 Pd/H-FER 206 2-44 Pd/ZrO₂ 42 28 2-45 Pd/WO₃/TiO₂ 44 36 2-46 Pd/MgO 1 1 2-47Pd/Mg—Al 1 1

Table 6 below shows the NO_(x) conversions for catalysts 2-1 through2-47 tested at various temperatures with 1% H₂ in feed. The activity onmost of the catalyst is significantly increased with the increased H₂concentration. Even at 100° C., most of the catalysts show >90% NO_(x)conversion. The lowest activity was found on MgO supported catalysts.

TABLE 6 NO_(x) conversion (%) of catalysts as a function of reactiontemperature at 1% H₂ Sample Sample ID Name 100° C. 125° C. 150° C. 175°C. 200° C. 2-1 Pt/ 91 98 94 83 74 Mg—Y 2-2 Pt/ 97 98 98 91 81 H—Y 2-3Pt/Beta 69 98 98 98 94 2-4 Pt/H- 96 96 88 80 71 CHA 2-5 Pt/H- 97 96 8677 68 ZSM-5 2-6 Pt/H- 96 96 86 78 70 MOR 2-7 Pt/H- 94 94 88 83 76 FER2-8 Pt/ZrO₂ 96 92 87 78 68 2-9 Pt/WO₃/ 98 95 89 79 67 TiO₂ 2-10 Pt/MgO 311 28 59 80 2-11 Pt/ 14 62 98 97 97 Mg—Al HT 2-12 Pt/Pd_8:1/ 98 98 98 8978 H—Y 2-13 Pt/Pd_8:1/ 14 59 98 98 97 H-Beta 2-14 Pt/Pd_8:1/ 95 94 85 7563 H-CHA 2-15 Pt/Pd_8:1/ 98 96 85 74 62 H-ZSM-5 2-16 Pt/Pd_8:1/ 98 89 7762 47 H-MOR 2-17 Pt/Pd_8:1/ 96 95 87 77 65 H-FER 2-18 Pt/Pd_8:1/ 96 9281 66 48 ZrO₂ 2-19 Pt/Pd_8:1/ 98 98 86 74 64 WO₃/TiO₂ 2-20 Pt/Pd_4:1/ 9898 98 92 85 H—Y 2-21 Pt/Pd_4:1/ 9 33 64 98 98 H-Beta 2-22 Pt/Pd_4:1/ 9893 76 57 40 H-CHA 2-23 Pt/Pd_4:1/ 98 98 81 67 58 H-ZSM-5 2-24 Pt/Pd_4:1/NA NA NA NA NA H-MOR 2-25 Pt/Pd_4:1/ 91 92 84 74 62 H-FER 2-26Pt/Pd_4:1/ 98 94 86 73 55 ZrO₂ 2-27 Pt/Pd_4:1/ 98 98 88 78 72 WO₃/TiO₂2-28 Pt/Pd_4:1/ 5 19 36 55 85 MgO 2-29 Pt/Pd_4:1/ 28 86 97 96 94 Mg—Al2-30 Pt/Pd_2:1/ 90 98 98 92 85 H—Y 2-31 Pt/Pd_2:1/ 13 35 69 98 95 H-Beta2-32 Pt/Pd_2:1/ 98 95 67 46 39 H-CHA 2-33 Pt/Pd_2:1/ 98 98 75 63 59H-ZSM-5 2-34 Pt/Pd_2:1/ 98 90 69 57 54 H-MOR 2-35 Pt/Pd_2:1/ 97 96 89 7970 H-FER 2-36 Pt/Pd_2:1/ 97 96 95 88 79 ZrO₂ 2-37 Pt/Pd_2:1/ 98 98 90 8781 WO₃/TiO₂ 2-38 Pd/H—Y 47 88 90 89 87 2-39 Pd/Beta NA NA NA NA NA 2-40Pd/H- NA NA NA NA NA CHA 2-41 Pd/H- NA NA NA NA NA ZSM-5 2-42 Pd/H- 5369 42 40 49 MOR 2-43 Pd/H- 28 58 66 76 79 FER 2-44 Pd/ZrO₂ 96 89 89 8377 2-45 Pd/WO₃/ 97 96 95 93 89 TiO₂ 2-46 Pd/MgO 2 8 10 14 31 2-47 Pd/ 26 9 16 43 Mg—Al

FIGS. 4-13 provide certain testing data for several of the abovecatalyst samples. In each figure, the Sample ID number is provided foreach catalyst sample show in the figure. FIG. 4 shows the NO_(x)conversion over H—Y supported Pt/Pd catalysts at 125° C. at 1% H₂ as afunction of feed condition and Pt/Pd ratio. This figure illustrates theeffect of CO addition and C₃H₆ addition on NO_(x) conversion. With Feed1 (no CO, no HC), the NO_(x) conversions are very high (>90%) on allcatalysts. Adding 500 ppm CO significantly decreases the NO_(x)conversion, and the degree of decreases is linearly proportional to thePt content up to Pt/Pd=2:1. On the other hand, addition of 100 ppm C₃H₆shows a minimal decrease in NO_(x) conversion for all Pt and Pt/Pdcatalysts (NO_(x) conversion >90%) but a drastic decrease on the Pdcatalyst (conversion=30%).

FIG. 5 shows the NO_(x) conversion over H—Y supported Pt/Pd catalysts asfunction of reaction temperature with Feed 1. FIG. 6 shows the NO_(x)conversion over H—Y supported Pt/Pd catalysts as function of reactiontemperature with Feed 2. FIG. 7 shows the NO_(x) conversion over H—Ysupported Pt/Pd catalysts as function of reaction temperature with Feed3.

FIG. 8 shows the NO_(x) conversion over WO₃/TiO₂ supported Pt/Pdcatalysts at 125° C. at 1% H₂ as a function of feed condition and Pt/Pdratio. With Feed 1 (no CO, no HC), all NO_(x) conversions are above 87%.Adding 500 ppm CO significantly decreases the NO_(x) conversion on allPt/Pd catalysts, but the decrease is less on the Pd catalyst. On theother hand, addition of 100 ppm C₃H₆ shows a minimal decrease in NO_(x)conversion for all catalysts.

FIG. 9 shows the NO_(x) conversion over WO₃/TiO₂ supported Pt/Pdcatalysts as function of reaction temperature with Feed 1. FIG. 10 showsthe NO_(x) conversion over WO₃/TiO₂ supported Pt/Pd catalysts asfunction of reaction temperature with Feed 2. FIG. 11 shows the NO_(x)conversion over WO₃/TiO₂ supported Pt/Pd catalysts as function ofreaction temperature with Feed 3.

FIG. 12 shows the effect of CO on NO_(x) conversion at 150° C. over anumber of catalyst families. FIG. 13 shows the effect of C₃H₆ on NO_(x)conversion at 150° C. over a number of catalyst families.

It is clear that CO has a more negative impact on Pt catalysts and Pt/Pdcatalysts and less impact on Pd catalysts. On the other hand, HC has aless impact on Pt catalysts but more on Pd catalysts. Pd/H—Y is the bestcatalyst tested with a feed containing CO, while Pt/H—Y and Pt/H-MOR arethe most active catalyst with a feed containing C₃H₆.

The use of the terms “a,” “an,” “the,” and similar referents in thecontext of describing the materials and methods discussed herein(especially in the context of the following claims) are to be construedto cover both the singular and the plural, unless otherwise indicatedherein or clearly contradicted by context. Recitation of ranges ofvalues herein are merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range,unless otherwise indicated herein, and each separate value isincorporated into the specification as if it were individually recitedherein. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate the materials and methods and does not pose a limitation onthe scope unless otherwise claimed. No language in the specificationshould be construed as indicating any non-claimed element as essentialto the practice of the disclosed materials and methods.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe present disclosure. Thus, the appearances of the phrases such as “inone or more embodiments,” “in certain embodiments,” “in someembodiments,” “in one embodiment,” or “in an embodiment” in variousplaces throughout this specification are not necessarily referring tothe same embodiment of the present disclosure. Furthermore, theparticular features, structures, materials, or characteristics may becombined in any suitable manner in one or more embodiments.

Although the embodiments disclosed herein have been described withreference to particular embodiments it is to be understood that theseembodiments are merely illustrative of the principles and applicationsof the present disclosure. It will be apparent to those skilled in theart that various modifications and variations can be made to the methodand apparatus of the present disclosure without departing from thespirit and scope of the disclosure. Thus, it is intended that thepresent disclosure include modifications and variations that are withinthe scope of the appended claims and their equivalents, and theabove-described embodiments are presented for purposes of illustrationand not of limitation.

What is claimed is:
 1. An emission treatment system for selectivelyreducing NOx compounds, the system comprising: a hydrogen generator; andan H₂-SCR catalytic article comprising a substrate and an H₂-SCRcatalyst composition, the hydrogen generator being in fluidcommunication with, and upstream of, the H₂-SCR catalytic article;wherein the H₂-SCR catalyst composition comprises a platinum group metalcomponent with a metal loading ranging from 0.1% to 1% by weight of theH₂-SCR catalyst composition supported on a support consisting of (i) ahydrogen form of zeolite, (ii) a metal oxide selected from the groupconsisting of zirconia, titania, magnesia, and combinations thereof, or(iii) combinations of (i) and (ii); and at least one of (a) a dieseloxidation catalyst (DOC) catalyst composition; and (b) a lean NOx trap(LNT) composition, wherein when the LNT composition is present, thesystem comprises a lean NOx trap (LNT) catalytic article comprising asubstrate and the LNT catalyst composition, the LNT catalytic article influid communication with, and downstream of, the H₂-SCR catalyticarticle, and wherein when the DOC catalyst composition is present, theDOC catalyst composition is present in a zoned catalyst coating on theH₂-SCR catalytic article with an upstream zone comprising the H₂-SCRcatalyst composition and a downstream zone comprising the DOC catalystcomposition.
 2. The emission treatment system according to claim 1,further comprising a low temperature NOx adsorbent (LTNA) catalystcomposition present in the zoned catalyst coating.
 3. The emissiontreatment system according to claim 2, wherein, in the zoned catalystcoating, the LTNA catalyst composition is incorporated into the upstreamzone comprising the H₂-SCR catalyst composition, incorporated into thedownstream zone comprising the DOC composition, or positioned in amiddle zone between the upstream zone comprising the H₂-SCR catalystcomposition and the downstream zone comprising the DOC composition. 4.The emission treatment system according to claim 1, further comprising alow temperature NOx adsorbent (LTNA) catalytic article comprising asubstrate and a LTNA catalyst composition, the LTNA catalytic article influid communication with the H₂-SCR catalytic article and the hydrogengenerator.
 5. The emission treatment system according to claim 4,wherein the LTNA catalytic article is positioned downstream from theH₂-SCR catalytic article or positioned upstream from the H₂SCR catalyticarticle and the hydrogen generator.
 6. The emission treatment systemaccording to claim 1, wherein the LNT catalyst composition comprises aNOx sorbent and a platinum group metal component dispersed on arefractory metal oxide support.
 7. The emission treatment systemaccording to claim 1, wherein the H₂-SCR catalytic article is closecoupled.
 8. The emission treatment system according to claim 1, whereinthe platinum group metal component is platinum, palladium, or acombination thereof.
 9. A method for treating an exhaust streamcontaining NOx, comprising passing the exhaust stream through theemission treatment system of claim
 1. 10. The method according to claim9, wherein the exhaust stream has a temperature that is about 200° C. orlower, about 175° C. or lower, about 150° C. or lower, about 125° C. orlower, or about 100° C. or lower.
 11. The emission treatment systemaccording to claim 1, further comprising a catalytic soot filter (CSF),a selective catalytic reduction (SCR) catalyst, an ammonia oxidationcatalyst (AMOX), or combinations thereof.
 12. The emission treatmentsystem according to claim 11, wherein the SCR catalyst comprises a basemetal-containing 8-ring small pore molecular sieve.
 13. The emissiontreatment system according to claim 12, wherein the SCR catalystcomprises an iron and/or copper-containing 8-ring small pore molecularsieve.
 14. The emission treatment system according to claim 13, whereinthe molecular sieve is a zeolite having a structure selected from thegroup consisting of AEI, AFT, AFX, CHA, EAB, EM, KFI, LEV, SAS, SAT, andSAV.
 15. The emission treatment system according to claim 14, whereinthe molecular sieve has a CHA crystal structure.
 16. A method fortreating an exhaust stream containing NOx, comprising: introducinghydrogen gas into the exhaust stream to form a hydrogen-treated exhauststream; passing the hydrogen-treated exhaust stream through an emissiontreatment system comprising an H₂SCR catalytic article comprising asubstrate and an H₂SCR catalyst composition, wherein the H₂SCR catalystcomposition comprises a platinum group metal component with a metalloading ranging from 0.1% to 1% by weight of the H₂-SCR catalystcomposition supported on a support consisting of (i) a hydrogen form ofzeolite, (ii) a metal oxide selected from the group consisting ofzirconia, titania, magnesia, and combinations thereof, or (iii)combinations of (i) and (ii); and at least one of (a) a diesel oxidationcatalyst (DOC) catalyst composition; and (b) a lean NOx trap (LNT)composition, wherein when the LNT composition is present, the systemcomprises a lean NOx trap (LNT) catalytic article comprising a substrateand the LNT catalyst composition, the LNT catalytic article in fluidcommunication with, and downstream of, the H₂-SCR catalytic article, andwherein when the DOC catalyst composition is present, the DOC catalystcomposition is present in a zoned catalyst coating on the H₂-SCRcatalytic article with an upstream zone comprising the H₂-SCR catalystcomposition and a downstream zone comprising the DOC catalystcomposition.
 17. The method according to claim 16, wherein the platinumgroup metal component is platinum, palladium, or a combination thereof.18. The emission treatment system according to claim 1, wherein thehydrogen generator is selected from the group consisting of on boardhydrogen, hydrogen produced from alcohol reforming, hydrogen producedfrom ammonia decomposition, and combinations thereof.